The present invention relates to improvements in secondary seals for a floating roof storage tank, and specifically to the provision of a secondary seal that provides a gas tight additional seal between the tank shell and the floating roof rim.
Current air quality control regulations require that floating roof storage tanks be provided with both a primary seal and a secondary seal to control the emission of volatile components and fumes from liquid stored within the floating roof storage tank. The primary seal closes the opening between the floating roof rim and either the tank shell or a metal shoe sliding on the inner surface of the tank shell. The secondary seal closes the space between the tank shell and the floating roof rim above the primary seal. Examples of floating roof storage tanks in which the secondary seal of the present invention is useful are illustrated in U.S. Pat. No. 2,754,026 granted July 10, 1956 to J. H. Wiggins, U.S. Pat. No. 2,802,591 granted Aug. 13, 1957 to J. H. Wiggins, U.S. Pat. No. 3,043,468, issued July 10, 1962 to F. W. Horner, Jr. and U.S. Pat. No. 3,307,733, granted Mar. 7, 1967 to W. L. De Bock.
Secondary seals for floating roof storage tanks have been provided heretofore, and exemplars thereof are illustrated in U.S. Pat. No. 2,427,171 granted Sept. 9, 1947, to J. H. Wiggins and U.S. Pat. No. 4,154,359 granted May 15, 1979 to B. E. Bissett. The secondary seals illustrated in the foregoing patents do not teach gas tight connections to the floating roof and, indeed, the secondary seal of U.S. Pat. No. 2,427,171 is not even connected to the floating roof. While the secondary seal of the Bissett patent does close the space between the floating roof and the tank shell, it is inadequately supported and it makes no provision for access to the annular space between the primary and secondary seals. Furthermore, the upper edge of the Bissett secondary seal is susceptible to snagging on surface irregularities on the inside of the tank shell.